Protective fuse for furnaces and the like



oct. 3o, 1934. P, H, @ARR 1,979,098

PROTECTIVE FUSE FOR FURNAGES AND THE LIKE Filed July 29, 1953 3l 30 28 I C A l I 24 l?. 26 25 24a 7 25 5 l I /ll/ a =2B 4 4 @2027 25 lzb Z ze lnvehtor: philip H. Clar'k,

H is AttovneJ.

Patented ct. 30, 1934 Anarran stares PROTECTIVE FUSE FOR FURNACES AND Electric Company, York a corporation of New Application July 29, 1933,l Serial No. 682,816

6 Claims.

"This invention relates to fuses for furnaces'and vthe like, and it has for -its object the provision of improved means for cutting olf the heat supply toI the furnace upon the occurrence of a predetermined maximum temperature in the furnace.

While not limited thereto, this invention has particularapplication to high temperature electric furnaces, such as are used in the heat treatment of metals and the like. Such furnaces are commonly operated at temperatures ofA 800 F. and 900 F. and in some instancesare operated at even higher temperatures.

`In electricalfurnaces, and also in gas and oil fired furnaces, it is desirable to protect the heating-equipment from excessively high tempera- 'tures which, if they were allowed to occur, would 'result in `damage to the heating equipment. At timesnexcessive temperaturescan occur because lof the failure of somev part of the control provided for theheaters. It is also desirable to protect the work in the furnace from over heating, because excessive temperatures in some cases will absolutely' ruin the materialbeing treated. Moreover, a protection against excessive temperatures is desired in many'cases for the furnace itself, especially where the furnace is constructed of materials which will not withstand overheating. -YFuses' have been provided heretofore for controlling furnace heating equipment. These fuses 'are arranged to' be exposed to the-heat Yin the furnace,'and function'toshut off theheat supplied to thefurnace, in' the eventthe furnace temperature rises to a value `suiiicient to fuse the material of which theA fuse is made.

Some difficultyhas been experienced with the fuses heretofore known, because of the tendency for the fusible 'materialto oxidize long before it is called upon to shut off the heat. This condition, of course, often results in failure of the control to shut off theheat in the event of an excessive temperature in vthe furnace.

In accordance with this invention, the fusible member is exposed to the heat in the furnace, and is enclosed by a casing in which is placed an enveloping atmosphere for the fusible member. Nitrogen or some other inert gas may be used to envelope the' fusible member, or the casing may be substantially evacuated of all air and gas.

I have found that the fuse arranged in accordance with this invention may be used successfully in furnaces operating at temperatures as high as 1200 F.

For a more complete understanding of this invention, reference should be had to the accomypanying drawing'in which Fig. 1 is an elevation of a fuse arranged vin accordance with this invention; Fig. 2 is an enlarged sectionalelevation of the fuse shown in Fig. 1, parts being`--broken away; Fig. 3 is an' enlarged horizontalr sectional View of the fuse Shown in Figs. land 2, parts beingbroken away; and Fig. 4 isa diagrammatic View showing an electric furnace equipped With a protective fuse embodying this invention.

Referring to the'drawng, the fuse 10 in one form of this invention-comprises a fusible member 1l supported in a suitable elongated casing 12. Thefusible member comprises a relatively short strip or link, as shown, formed ofa suitable fusible material, such as a gold-cadmiumalloy-havmg a gold contentof approximately70%, or-a goldzinc alloy having a gold content of approximately It will be understood, of course, thatother Lsuitable alloys may be-used, the selection of the alloy depending upon the temperature at which it is desired the fuse shall function to shut oif the heat. The casing 12 will be madeof a suitable heat resisting material, such as calorized'steel, or a nickel-chromium alloy.

The fusible link l1 is supported byzmeans of a pair of lead members 13, which in turn are supported in the casing bymeans of a plurality of heat refractory, electrical insulators 14.

,The link 11 may be and as shown is secured to the leads 13 by compressing the leads upon the ends of the link. This may be accomplished by inserting the ends of the link'into recesses vpfovided for them in the leads, and then swaging the leads upon the link.

The members 14`may be made of any suitable refractory insulating material, such as porcelain. rEhese members 14 are each provided'with four longitudinal apertures 15, 16 and 17 and 18. The apertures 15 and 16 are positioned 180 apartfand so are the apertures 1'7 and 18 arranged -180-apart. The two pairs of apertures comprising the apertures 15 and 16, and 17 and 18 are arranged' at right angles to each other.

The apertures 15 and 16vreceive-a U-shaped clamping member l20 threaded through these apertures sov as tohold theinsulators lll assembled-in end to end relation. 'The insulators vv14I are interlocked witheach other-'so as to ypreventrelative rotative movement between them. *For this purpose, each insulator Vis provided with aftongue 14a which is 'received inafgroove leb provided for-it in the adjacent insulator.

The inner insulator 14, that is, the insulator shown at the extreme rightof the casing 12, as viewed in the figures hasy a form somewhat different from the remaininginsulatorsin that it is sageways 28 surrounding these leads.

provided at its inner end with a transverse groove 21 which receives the transverse central portion 22 of the U-shaped clamping member 20. It will be understood that in assembling the insulators with the clamping member, the innermost insulator 14 will rst'be threaded upon the clamping member, and then the desired number of insulators 14 will be threaded upon the clamping member in end to end relation, as clearly shown in Fig. 1. 1f desired, all of the insulators may be made up in the same shape as the inner insulator. This may lessen the cost of production; .Y Y

The outermost insulator 14 is spaced somewhat from the next adjacent insulator to provideV a space 23, as clearly shown in Figs. 2 and'3, for a purpose which will be set forth hereinafter.

The leads 13 supporting the fuse ll are threaded through the remaining pairliof apertures 17 and'l8 and extend completely through the abutting series of insulators positionedon the right ofthe space H23 and terminate withtheir ends projecting into this space. i

Suitable leads` 24 are provided whereby the fusible member 1l may be connected in an external electrical circuit which may be the circuit to be controlled, `or a controlling circuit for thel circuit to be controlled. As shown, the leads 24 are tions of the leads 13 projecting into the space 23 by means of sleeve-like connector members 25, each of which is provided with a centrally arranged aperture 26 receiving the projecting portions of the two sets ofv leads. Suitable set screws 27 are threaded in the .connector members and terminate'in the'passageways 25 so as to bear against the portions of the leads which are received in the passages and thereby secure the two pairs of leads together with very good electrical and mechanical connections.

The outer ends of the leads 24 are passed to the exterior of the casing 12 through suitable apertures 28 provided for themin the outer'wall 12b of the casing.

The leads 24 where they emerge from the casing are surrounded by layers 30 of a suitable sealing material arranged to Vhave fluid-tight joints both with the leads 24 and with the walls of the pas- As clearly shown in Fig. 3, the passageways 28 have diameters considerably larger than the diameters of the leads 24 so as to provide ample space for the sealing material 30.

The sealing layers 30 preferably will be formed of a suitable vitreous material, such as a suitable lead glass.

The outerends 24a terminate in a suitable terminal box 31 where electrical connections are established with a circuit`32, which as previously indicated may be a circuit to be controlled or a controlling circuit for the circuit to be controlled. The ends 24a of the leads 24 are electrically connected with the electrical conductors 32 by means of suitable connector members 33 similar to the connector members 25.

The inner end of the casing 12 is closed by means of a suitable head 34 having a fluid tight joint 35 with the casing. This joint 35 may be and preferably will be a welded joint.

Preferably, and as shown, the casing 12 will be formed of a plurality ofk detachable sections comprising'the innercasing portion 12a housing the insulators 14 and the fusible member 11, the outer head member casing 12b and an intermediate section 12C mechanically connecting the head with the casing proper 12a. screw-threaded connections will be provided between these members.

As previously pointed out, the casing 12 will be filled with a selected atmosphere which may be nitrogen or some other inert gas, or the casing may be substantially evacuated of air and gas.

In assembling the fuse, the leads 24 will be threaded through the apertures 28 provided for them in the head 12b and the space between the leads and the walls of these apertures will be filled with the glass sealing material 30. These seals may be formed by threading tubes formed of glass on the lead members and then placing the glass sleeves in the apertures 28. Then the glass sleeves are heated until softened, after y which pressure is applied to the ends of the sleeves so as to force the glass into intimate contact with fthe leads and with the walls of the passageways 28. Then the glass is allowed to cool. It has been found that this glass will firmly adhere both Y to the leads and to these walls so as to provide fluid-tight joints both with the leads and the walls.

maining apertures 17 and 18 of this series of insulators, and will be properly positioned with respect tothe insulators so thatrthe fuse will be supported in spaced relation with respect to the inner insulator and so that the .outer ends of the leads will project from the outermost insulator 14 of this series. j

Then the connectors will be secured to the projecting portions of the leads by means of the set screws 27, .after which the outermost insulator 1,4 will be threaded upon the clamping member 20. Then the clamping member will be secured to the insulators by means of nuts 20a.

It will be observed in view of the foregoing operations that the insulators 14, the leads 13,

the fusible member 11 and the connectors 25 will j be assembled into a unitary structure.

Then the central casing portion 12o will be vthreaded upon the section 12b. And then the unitary structure comprising the insulators 14,

leads 13, fusible member 11 and connectors 25'.l

It will be understood that the casing 12a will be suiciently long toI provide the space for the fusible member 11 when the casingvv is thus assembled.

In some cases, it has been found that the small amountfof entrapped air in thecasing may be allowed to remain, the quantity not being suffi` cient to cause any material oXidiZation of the fusible member l1.v The glass seals .at the outer end of the fuse and the seal at the inner. end of the casing-prevent the admission of any Preferably, fluid-tight,r

more air into the casing. However, when a fuse is to be used in very high temperature furnaces, it is advisable to exhaust the air from the casing. This air may be exhausted in any suitable manner well known in the art. If desired, the air may be exhausted and replaced with pure nitrogen, or some other suitable inert gas.

The air can be exhausted conveniently by placing a few drops of gasoline in the casing, or by placing on the casing oil or some metal, such as copper, magnesium and the like, which will consume the oxygen of the air in the casing when the fuse is heated up.

As shown, the fuse l0 is applied to an electrically heated furnace 37. The fuse l0 is mounted in a wall 38 of the furnace chamber, the fuse being inserted through a suitable aperture 40 provided for it in the wall so that its inner end extends into the heating chamber 41 of the furnace. In other words, the fuse 10 is mounted in the wall so that the fusible member l1 is exposed to the heat in the furnace chamber.

The furnace is heated by means of a suitable heating resistance element 42 which is supplied from a suitable source of electrical supply 43. The resistance element 42 is connected with the supply source through a suitable contactor 44, the energizing coil of which is connected with the electrical supply source 43 through the fuse lO. When the operating coil is energized through the fuse, the contactor is held closed so as to connect the resistance element 42 with its supply source. Under normal conditions of operation the operating coil for the contactor 44 will thus be maintained closed through the fuse so as to maintain the connections between the supply source and the resistance element. Upon the occurrence of a temperature in the furnace approaching the maximum safe temperature of operation, the fusible element 11 will melt, thereby opening the energizing circuit for the operating coil of the contactor, which thereupon will permit the contacter to drop out to disconnect the resistance heating element 42.

In the event it is necessary to replace the fuse, the casing 12a will be unthreaded from the portion 12o, and a new fusible member l1 including the two leads 13 to which the fuse will be attached is assembled with the leads 24 in the manner previously described.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A fuse for electric furnaces and the like comprising an elongated casing arranged to be inserted through an aperture in a furnace wall so that the inner end of said casing is exposed to the ambient temperature of the heating cham- 1oer of said furnace, an electrically insulating, heat refractory supporting member within said casing, a fusible member supported by said supporting member in said inner end of said casing so that when said casing is inserted in said aperture, said fusible member is exposed to the ambient temperature of said furnace, leads for said fusible member projecting from the outer end of said casing, means for sealing said leads where they emerge from said casing and a selected protective atmosphere within said casing about this fusible member.

2. A fuse for electric furnaces and the like comprising an elongated casing, an elongated heat refractory supporting member arranged in said casing so as to leave a space at one end of said casing, said supporting member being provided with longitudinal apertures, leads supported in said apertures projecting into said space, a fusible member within said space electrically connected with said leads and supported thereby, vitreous sealing material surrounding said leads where they enter said casing and a selected atmosphere in said casing.

3. A protective fuse for electric furnaces and the like comprising an elongated casing, a plurality of electrically insulating heat refractory supporting members in said casing in abutting relation with each other, said members having registering apertures, leads threaded in said apertures and supporting a fusible metallic member across the inner end of said members, said leads projecting from the apertures at the other end of said support and emerging from said casing, a

glass sealing material surrounding said leads? Where they emerge from said casing and having iiuid tight joints both with said leads and with said casing and a selected atmosphere in said casing.

4. A fuse for electric furnaces and the like comprising an elongated casing adapted to be inserted in an opening provided for it in a furnace wall, aplurality of heat refractory electrically insulating supporting members in said casing in abutting relation with respect to each other and arranged to leave a space in the inner end of said casing, said supporting members be-.

ing provided with sets of registering apertures, a U-shaped clamping member threaded through a pair of said apertures so as to secure said supports in abutting relation, a pair of leads threaded through the other two apertures and projecting into said space at the inner end of said casing a fusible member in said space electrically connected with said leads, and supported thereby,

a pair of leads projecting from the other end of said casing, means within said casing detachably connecting said second named leads with said nrst named leads, layers of glass sealing material surrounding said second-named leads where they 3; emerge from said casing and having fluid-tight joints both with said leads and said casing, and a selected atmosphere in said casing.

5. A fuse for electric furnaces and the like comprising an elongated casing adapted to be inserted through an aperture in a furnace wall, said casing comprising a pair of sections and a connection between said sections whereby they can be easily separated, a fusible member supported in the inner end of said casing so as to be exposed to the heat of said furnace when said fuse is inserted in said aperture, leads for said fusible member projecting from the opposite end of said casing, means for sealing the leads where they emerge from said casing, means within said casist on the exterior of saidiurnace wall, Vlayers of glass surrounding said leads where they emerge from said casing so as to. provide iiuid-tight joints between said leads and said casing, electrical connection members between said first named and said second named pairs of Yleads arranged so that said pairs of leads can be easily connected and disconnected, and a selected atmosphere in this casing.

, PHILIP I-I.'CLARK. 

